This invention relates to an infrared shielding lamination, and more particularly to an infrared shielding laminated body which is transparent to visible light, but is capable of effectively shutting out infrared rays and near-infrared rays.
If use is made of window glass which is transparent to visible light but effectively excludes infrared rays, thermal insulation provided by the car windows will be accordingly improved. Specifically, the infrared rays will be prevented from reaching the interior of the car, whereby the cooling performance of the car will be improved accordingly. As a result, the amount of power required for air conditioning the car will be reduced.
Conventionally, window glass has been made transparent to visible light but capable of eliminating infrared rays by coating the glass with an infrared ray shielding substance. Such window glass, however, is unsatisfactory in its transparency to visible light, its ability to exclude infrared rays, the durability of its physical and chemical qualities and other characteristics.
In the prior art an ordinary glass plate which is transparent to visible light is covered by a single coating layer of infrared shielding substance, such as Indium-Tin-Oxide (In.sub.2 O.sub.3 --SnO.sub.2) (hereinafter abbreviated as "ITO"). A family of semiconductor substances represented by ITO show fairly good shielding capability for the wavelengths in the infrared range longer than 13000 angstroms, which range is slightly separated from the spectrum of visible light, and these substances can be readily produced. These semiconductor substances, however, show inadequate shielding capability for the near-infrared range from 7000 to 13000 angstroms. Sunlight and other ambient light have a distribution of relatively strong energy over the whole range of the near-infrared spectrum, and therefore disadvantageously conventional infrared-shielding window glass allows the passage of a relatively large amount of thermal energy into an enclosed space, such as the interior of a car.
Up to now, attempts have been made to improve the optical characteristics of the ITO coating by extending its cut-off wavelength up to the near-infrared spectrum range. However, it has not been possible to produce such optically improved ITO without difficulty. What is worse is that the semiconductor material produced in this way shows poor transparency to visible light. For these and other reasons, it has been very difficult to obtain a coating material satisfactorily meeting the requirements both for transparency to visible rays and for shielding of infrared and near-infrared rays. The infrared shielding relying on a single ITO coating layer applied to a glass plate necessitates a large coating thickness, for instance, up to 3000-10000 angstroms. A large coating thickness, however, disadvantageously suffers a drastic decrease in its mechanical strength and the thick-coated layer is thus easy to break or peel off. This is because absorption of infrared rays in the thickness of the coating layer causes a thermal stress therein. When a glass with a thick infrared shield coating applied thereto is used as a window glass in a car, a mechanical stress is most liable to appear in the thickness of the infrared shield coating during the processing thereof or later during use. The rate of increase in these thermal and mechanical stresses rises with increasing thickness of the coating and accordingly the mechanical strength of the coating decreases inversely with the thickness of the coating.